1. Field of the Invention
This invention relates to a soil conditioner which consists essentially of inorganic materials and, according to need, may contain microorganisms capable of eliminating detrimental effects of harmful microorganisms more effectively from the rhizosphere of a crop.
2. Description of the Prior Art
The purposes of soil improvement include the chemical conditioning of the soil mainly comprising the adjustment of pH and the balancing of inorganic nutrients, the physical conditioning of the soil mainly comprising the improvement of water permeability, air permeability and water retention properties, and the improvement of the ecological system concerning the activity of useful microorganisms in the soil.
In the prior art, a variety of soil conditioners are known. However, they are all effective in accomplishing one or two of the aforesaid purposes, and no soil conditioner that can comprehensively answer all of the aforesaid purposes is known as yet.
For example, it is common practice to improve a soil by use of slag or coal ash. Since slag and coal ash are strongly alkaline, they serve for the improvement of an acid soil, but tend to damage crops by alkali soil (which will be hereinafter referred to as alkali damage). If the amount of slag or coal ash added is decreased to avoid such a disadvantage, the soil will return to an acid state in a short period of time and the effect of the slag or coal ash will not last satisfactorily.
Moreover, slag is also disadvantageous in that the soil to which slag has been applied becomes hard because of the hydraulic nature of the slag.
Furthermore, slag and coal ash have the additional disadvantage of having low fertilizer-retaining power. In the soil to which they have been applied, therefore, the fertilizers tend to be carried away by rainwater or sprinkled water.
As a method for the physical conditioning of the soil, it is well known to disperse and mix foamed polystyrene particles in a soil. However, this only serves to provide the soil with voids. Accordingly, in case of a heavy rain or an abundant water sprinkling, the draining ability of the soil is unduly enhanced owing to the presence of such voids. As a result, the foamed polystyrene particles may often rise to the surface of the soil to lose its soil-conditioning effect and, moreover, cause the fertilizers to be carried away together with them.
A soil activator comprising soil microorganisms adsorbed to vermiculite or the like is disclosed, for example, in Japanese Patent Laid-Open No. 40723/'80. However, this is not satisfactorily effective in decomposing or adsorbing harmful substances (including ethylene and other hydrocarbons detrimental to crops, certain hydrocarbons and hydrogen sulfide which promote the propagation of harmful microorganisms) and thereby inhibiting the detrimental effects thereof. Moreover, this soil activator is also inadequate for the prevention of damage caused by continuous cropping.
At present, the development of various types of soil conditioners has made it relatively easy to achieve the chemical and physical conditioning of the soil. However, it is the existing state of the art that a soil conditioner having an overall effect including an improvement of the ecological system of the soil has not been provided as yet. In particular, the prevention of damage caused by continuous cropping is the most important problem with modern agriculture is confronted. In order to solve this problem, a soil conditioner having an overall effect as described above is required, but none of the prior art soil conditioners can perform such a function. Thus, there is a strong demand for the development of a soil conditioner having an overall effect which is especially effective in the prevention of damage caused by continuous cropping.